#define _CRT_SECURE_NO_WARNINGS	

#include<stdio.h>

int Sum(int x, int y)
{
    int count = 0;
    for (int i = x; i <= y; i++)
        count += i;
    return count;
}

int main()
{
    int n;
    scanf("%d", &n);
    double sum = 0;
    for (int i = 1; i <= n; i++)
    {
        sum += 1.0 / Sum(i, 2 * i - 1);
    }
    printf("%.6f", sum);
    return 0;
}